We halted there for the night, sleeping for six hours, a long luxury upon the road, though this rest was broken twice by challenges from half-seen mounted parties who had found our bivouac. Afterwards we wandered among more small ridges until the dawn showed gentle valleys of sand with strange hills of lava hemming us about. The lava here was not the blue-black cinder-stone of the fields about Rabegh: it was rust-coloured, and piled in huge crags of flowing surface and bent and twisted texture, as though played with oddly while yet soft. The sand, at first a carpet about the foot of the dolerite, gradually gained on it. The hills got lower, with the sand banked up against them in greater drifts, till even the crests were sand-spattered, and at last drowned beyond sight. So, as the sun became high and painfully fierce, we led out upon a waste of dunes, rolling southward for miles down hill to the misty sea, where it lay grey-blue in the false distance of the heat.